The major objectives of the proposed research are fourfold: (1) to define the most suitable source, the optimal conditions, and the participation of different human leukocyte subpopulations for producing maximal amounts of a lymphokine-like T cell growth factor (TCGF); (2) to evaluate the utility of TCGF for cultivating different cells, including: (a) phenotypically- and functionally-defined T-cell subsets from the blood of healthy donors, (b) thymocytes from thymuses obtained from children during surgical procedures required to correct congenital heart defects, and (c) leukemic lymphocytes from children with acute lymphoblastic leukemia and leukemic myelocytes from adults with myeloid leukemia; (3) to characterize the phenotypic and functional properties of T-cells propagated initially by alloantigenic simulation and then grown in long-term TCGF-supplemented cultures; and (4) to explore the utility of the technology afforded by the fluorescence-activated cell sorter and murine monoclonal antibodies to isolate preselected antigen-specific T cell subsets; thereafter, such cells will be cultivated using TCGF and, at different intervals thereafter, evaluated for retention of immunocompetence. The significance of this project is derived partially from the potential clinical utility that may ultimately be realized by adoptive immunotherapy modalities and other regimens employing TCGF-propagated immunocompetent T-cells for treating patients with malignant and immune deficient diseases. The importance of this project is further substantiated by the information derived from in vitro studies employing distinct T-cell subsets for defining the role of thymus-dependent lymphocytes and their lymphokines as the primary mediators of cellular immunity.